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United States Department of Agriculture

Agricultural Research Service


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Title: Elevated CO2 and warming influence ecosystem carbon dynamics and evapotranspiration in a semi-arid grassland

item Heisler-white, Jana
item Pendall, Elise
item Williams, David
item Carrillo, Yolima
item Morgan, Jack
item Lecain, Daniel
item Newcomb, Joanne

Submitted to: Ecological Society of America Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 3/10/2009
Publication Date: 8/1/2009
Citation: Heisler-White, J., Pendall, E., Williams, D., Carrillo, Y., Morgan, J.A., Lecain, D.R., Newcomb, J. 2009. Elevated CO2 and warming influence ecosystem carbon dynamics and evapotranspiration in a semi-arid grassland. Ecological Society of America Proceedings. COS 07-3.

Interpretive Summary:

Technical Abstract: Ecosystem carbon dynamics are sensitive to rising CO2 concentrations and warming, but the combined effects of these global change drivers on ecosystem carbon uptake and loss remain a critical uncertainty. Northern mixed grass prairie is expected to be among the most responsive ecosystems to the effects of elevated CO2 because it is co-dominated by C3 and C4 plants and strongly sensitive to changes in soil water content. CO2 effects on this ecosystem may be enhanced or diminished when combined with rising temperatures, and response patterns are predicted to vary seasonally due to plant phenology and the distribution of rainfall events in this pulse-driven ecosystem. We measured net ecosystem exchange (NEE), ecosystem respiration (RE), and evapotranspiration (ET) intensively during the 2007-2008 growing seasons using static polycarbonate chambers fitted with open-path gas analyzers. Our objective was to characterize ecosystem carbon and water flux dynamics in response to the independent and interactive effects of elevated CO2 and warming, and frequent diurnal measurements allowed us to estimate daily rates and to quantify seasonal net fluxes. This research was conducted at the Prairie Heating and CO2 Enrichment (PHACE) experiment (Cheyenne, WY USA), which is a multi-factor global change experiment in which CO2 concentrations and temperature are factorially manipulated in a native grassland. Our results suggest that elevated CO2 stimulates both GPP and RE but the balance of these fluxes (NEE) varies seasonally. Combining warming with elevated CO2 reduces both RE and GPP (on average), but the effect on these two fluxes is non-linear. The strongest CO2 effect on GPP was observed in late May and at the end of the growing season, during which time plots under elevated CO2 maintained high GPP rates (-5.3 ±0.6 g C m-2 day-1) in contrast to the sharp decline that was observed under all other treatments (-2.0 ±0.5 g C m-2 day-1). At the end of the growing season, RE remained highest in CO2+ warming plots (2.7 ±0.1 g C m-2 day-1) as compared to all other treatment combinations (1.8 ± 0.5 g C m-2 day-1). These late season NEE differences contributed to elevated CO2 plots being a net carbon sink (-54 g C m-2) and elevated CO2+warming plots being a net carbon source (61.54 g C m-2). These results confirm the importance of CO2xwarming interactions on a semi-arid ecosystem with important implications for predicting carbon uptake and loss patterns under future globe change scenarios.

Last Modified: 10/17/2017
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